1. Field of the Invention
The present invention relates to a fluid filled vibration damping device that produces damping action by means of the damping characteristics exhibited by flow action of a non-compressible fluid sealed therein, such as a fluid filled vibration damping device used for an automobile engine mount, body mount, or differential mount.
2. Description of the Related Art
Fluid filled vibration damping devices are known as one type of damping device, such as a damping support unit or a damping connecting unit, for mounting between the component members of a vibration transmission system. This damping device has a construction wherein, as shown in JP-A-2002-206587 for example, a first mounting member is connected by a rubber elastic body to a cylindrical second mounting member that is disposed with a gap between it and the first mounting member; and a pressure-receiving chamber, part of the wall of which is comprised by the rubber elastic body, and an equilibrium chamber, part of the wall of which is comprised of an easily deformable flexible layer and in which a non-compressible fluid is enclosed, are respectively formed to either side of a partition member supported by the second mounting member, with these two chambers interconnected by an orifice passage. In this damping device, because damping action that would be difficult to obtain from the vibration-reducing effect or vibration-insulating effect of a rubber elastic body is here easily obtained based on the flow action of fluid, such as the resonance effect of the fluid flowing in the orifice passage, the application of such a damping device to an automobile engine mount or body mount has been contemplated.
Incidentally, in a damping device applied to an automobile engine mount or the like, because the frequency range of the vibration to be damped varies according to the vehicle driving conditions and the like, the device must provide a superior damping action with respect to multiple vibration frequencies falling over a wide range. For example, in the case of an automobile engine mount, in general, the device must provide damping action with respect to not only low-frequency vibration of around 10 Hz encountered with engine shake and middle-frequency vibration in the 15-30 Hz range that occur during engine idling or the like, but also to high-frequency vibration in the 80-120 Hz range, such as rumble during driving.
Accordingly, a fluid filled vibration damping device for accommodating this need is also described in JP-A-2-26336. In this damping device, a low-frequency orifice passage tuned to the low frequency range characteristic of engine shake and the like, a middle-frequency orifice passage tuned to the middle-frequency range characteristic of engine idling vibration and the like, and a high-frequency orifice passage tuned to the high-frequency range of driving noise and the like are disposed in a partition member, and deformable plates tuned to the frequency band of the associated orifice passage are disposed in the middle-frequency orifice passage and the high-frequency orifice passage.
In this type of damping device, when vibration in the low-frequency range is input, since the amount of flow in the middle-frequency and high-frequency orifice passages is restricted by the deformable plate while the amount of flow in the low-frequency orifice passage is secured, damping action is obtained based on the flow action of the fluid flowing in the low-frequency orifice passage. Furthermore, when vibration in the middle-frequency band is input, the low-frequency orifice passage becomes essentially clogged, but is prevented from acting as a high-powered spring by the flow action of the fluid flowing in the middle-frequency orifice passage or the fluid absorption effect attributable to the displacement or deformation of the deformable plate disposed therein, thereby giving rise to damping action.
However, in the fluid filled vibration damping device described in JP-A-2-26336, multiple deformable plates having mutually different tuning are prepared, and these plates are separately disposed in the fluid flow paths of the middle-frequency orifice passage and the high-frequency orifice passage. This increases the number of component parts and makes the device more complex and difficult to manufacture and assemble, thereby reducing manufacturing efficiency and increasing the cost of manufacture.
Furthermore, since the multiple, essentially round deformable plates are disposed side by side on essentially the same surface of the partition member, it is difficult to obtain a sufficient total effective surface area for the deformable plates on the partition member. Consequently, if sufficient total effective surface area for the deformable plates is to be obtained, the partition member, and therefore the damping device, must inevitably be increased in size.
Moreover, during assembly of the multiple deformable plates into the partition member, since it is difficult to determine the precise type of each deformable plate simply from observing its external appearance, there is a danger that one or more of the deformable plates may be erroneously assembled into the incorrect orifice passage.